Exemplary embodiments of the present invention relate to a method for producing a fiber composite component and to the use of the method.
Such methods, in which the fiber composite component is produced by infiltrating and curing of at least one textile component preform, wherein in at least one stage of the method pressure is exerted on the preform by means of an air-tight covering that covers the preform, are known from the prior art in many embodiments and are normally called “vacuum-supported” methods.
In the known methods for producing a fiber composite component (e.g. carbon fiber-reinforced plastic component), often a variety of supplementary agents or functional layers are required that become waste after the method has concluded. The known vacuum-supported methods include the required air-tight covering in the form of a plastic film.
Moreover, the pre-production of such plastic films, along with their handling as a (non-reusable) supplementary agent in the component production, represents a not insignificant portion of the production time and costs.
Finally, the use of plastic films in the production of a complicated shaped fiber composite component is frequently problematic or even unsuitable (e.g. for hollow components).
Accordingly, exemplary embodiments of the present invention are directed to a novel way to realize the “air-tight covering” in a production method of the type cited in the foregoing, and thus to reduce or eliminate in particular the aforesaid problems.
Proceeding from a method of the aforesaid type, this object is inventively attained in that the air-tight covering is formed from a resin film.
The resin film may be a cross-linkable thermoset plastic, in particular e.g. an epoxide resin system. This may be a material as is known per se from the field of fiber composite technology as “matrix material” for infiltrating a fiber material. Suitable materials are well known from the prior art and may be produced synthetically using polymerization, polyaddition, or polycondensation reactions. At least at the time of the application or addition of the resin film in the inventive “vacuum structure,” this resin film preferably has a liquid to semi-liquid consistency. In accordance with one preferred embodiment, the resin used for forming the resin film comprises at least two principle components, specifically the actual resin material that may be cured, e.g. by cross-linking and a curing agent that accomplishes or accelerates the curing process (“reaction resin”). In addition to resin materials based on epoxide resin (e.g. “RTM6” or the like), vinyl ester resins, phenol resins, or polyester resins may for instance also be used in the context of the invention, whether as material for the resin film and/or as matrix material for the textile component preform to be infiltrated.
If the resin film (e.g. an epoxide resin system) remains on the cured preform at the end of the production process, the waste formed in the prior art by the plastic films is advantageously prevented. The same is true if the resin film is used as such for infiltrating the preform disposed thereunder. Moreover, the invention provides a logistical advantage in that is implemented as devices for handling (conditioning, feeding, etc.) resin as “matrix material” of the fiber composite component to be in production devices in the type of interest here. In other words, when the invention is used it is not necessary to purchase and possibly adjust any plastic films; on the contrary, it is advantageously possible to use resin material that is already present, e.g. for infiltrating the preform, or that is additionally supplied for forming the resin film in system parts that are available per se.
Important parameters when selecting the resin may be e.g.: melting point, viscosity, reactivity, fusion temperature, and curing conditions.
With respect to the design of the preform (e.g. fabric, roving, meshwork, etc. made of fiber material), in the context of the invention known designs in the field of fiber composite technology may be used. The preform may be a single-layer preform or a multilayer preform (“laminate”). The preform may be “dry” or may already be pre-impregnated (“prepreg”) with matrix material (e.g. resin system).
As will become very clear, especially from the description of the exemplary embodiments, the inventive formation of the air-tight covering from a resin film surprisingly also provides useful options for vacuum-supported production of complicated fiber composite components, especially e.g. hollow components.
Moreover, the invention is advantageously compatible with the production principles for a number of established methods in fiber composite technology.
Thus, for instance, autoclave production, infiltration techniques such as VAP, hand lay-up methods, etc., as a rule are based on an external pressure acting on the covered preform to prevent porosities in the matrix and to attain favorable fiber volume. In the prior art, this is attained using a vacuum structure while employing the aforesaid plastic films as air-tight coverings. The inventive substitution of a resin film for the known plastic films permits the continued use of these known production principles and as stated in the foregoing furthermore provides additional advantages.
For instance, the chemical family of epoxide resins covers a large spectrum of reactivity, viscosity, and other physical properties. Such epoxide resins and other resin systems already used in fiber composite technology may be obtained in a wide range of designs and states, so that in the context of the invention a suitably air-tight film may be advantageously formed by selecting an appropriate resin. The fact that controlling pressure and temperature during the course of the production process provides the opportunity to deliberately influence in particular the consistency or viscosity of such resins is of substantial benefit for realizing the invention.
In series production of fiber composite components in accordance with the invention, the cycle times will be a function of the properties of the resin from which the covering resin film is formed (e.g. viscosity of the resin and its curing time). How long the tool is used is thus determined by such parameters. One estimate in this regard found that advantageously shorter cycle times than for the conventional methods could be attained with the inventive method.
In one embodiment the resin film is applied to the preform in the liquid to semi-liquid state.
The resin used may be a temperature-curing resin and/or epoxide resin system, whether e.g. a two-component resin or merely one resin component (e.g. pure epoxy chains).
Advantageously the resin may be applied with current film-applying surface techniques, e.g. by coating, spraying, rolling, smearing, applying by knife, or the like.
A suitable selection of the resin material and/or the “environmental conditions” (in particular on the free surface of the resin film), such as e.g. in particular temperature, humidity, etc., it is possible to ensure that the resin layer applied for instance directly to a preform surface already represents as it is, i.e. without further modification (e.g. without a change in consistency) an air-tight coating. Alternatively or in addition it is possible to change the environmental conditions of the aforesaid type after applying the resin in order to further improve (or to provide) gas-tightness of the resin film according to the specific resin material used.
In one embodiment the resin film is used in a “carrier-stabilized” form. In one special embodiment, to this end the resin film is initially pre-produced in a carrier-stabilized manner so that it is then placed onto the preform.
The term “carrier-stabilized” is intended to mean that the resin in question is first combined, not as is, but rather for instance in a separate pre-production process, with a carrier medium (e.g. made of fiber material). For instance, the carrier medium for this may be impregnated with the resin and where necessary pre-formed and/or cut and/or somewhat consolidated (e.g. using thermal partial curing), for instance to render the resin film easier to handle if it is a separately pre-produced carrier-stabilized resin film. Such a carrier-stabilized resin film is then first in the form of a separate semi-finished product so that it may then be placed e.g. directly onto the surface of the preform arranged on the tool (alternatively, e.g. a functional layer could also be added between preform and resin film).
As an alternative to separate pre-production of the carrier-stabilized resin film, e.g. first a carrier medium (e.g. dry fiber non-woven fabric) may be placed on the pre-form and then the resin may be applied, in a liquid to semi-liquid state, to the carrier medium such that the carrier medium is impregnated with the resin.
Regardless of whether the resin film forming the air-tight covering comprises only resin material or is used as a carrier-stabilized resin film, in accordance with one embodiment the consistency of the applied or placed resin film is deliberately influenced during the course of the production process by adjusting environmental parameters, such as for instance temperature or humidity, and/or by adding a catalyst.
In one embodiment such deliberate influence on the consistency is provided at least one time, and specifically at a time after the resin film has been applied or placed, but before the evacuation of the vacuum chamber embodied between resin film and tool surface.
In particular the addition of a catalyst is a simple and reliable option for causing the creation or stabilization of gas-tightness in a desired stage of the production method (e.g. during the infiltration of the preform) with a resin that is initially present in the liquid or semi-liquid state.
For instance, adding a catalyst that accelerates the otherwise very slow consolidation process or a consolidation process that otherwise occurs only at relatively high temperatures may have a desirable influence on the resin consistency.
In one refinement a catalyst is effectively used essentially only on the free resin film surface, i.e. the resin film surface facing away from the pre-form, so that essentially only the outermost surface areas of the resin film are cured or are cured more rapidly.
The latter refinement is possible, for instance, for an embodiment in which the preform is infiltrated using (at least some of) the resin film itself. The use of at least some of the resin material, which is inventively used in any case as an air-tight covering, as an “infiltration material” (matrix material) for the preform, as well, has the advantages e.g. that the preform is then infiltrated transverse to the preform plane, and thus rapidly, and that material of the resin film has an additional use, specifically as matrix material for the component to be produced.
In a more specific embodiment the preform is infiltrated using the resin film that is liquefied after the vacuum chamber is evacuated. Depending on the specific resin (system) selected, this liquefaction of the resin film may be effected e.g. using a deliberate increase in temperature.
In one preferred embodiment of the use of resin material of the resin film for infiltrating the preform is produced with a “resin excess.” To minimize porosity in the finished components, it is also possible to add, between the molding tool surface in question and the preform, e.g. an open-pored sacrificial layer that adds air and thus continues the negative pressure and that also may absorb residual air and/or excess resin (e.g. peel-ply, VAP membrane, or the like).
Alternatively or in addition to the use of resin material of the resin film for infiltrating the preform, this infiltration can occur in the “classic” manner, specifically using separately supplied resin. In this case it is generally advantageous when a so-called resin distribution medium (e.g. fiber non-woven fabric) is used that is inserted between the preform and the resin film e.g. as a functional layer provided for this. Separately supplied matrix material may flow through such a resin distribution medium in a manner known per se with low flow resistance parallel to the preform surface and after this lateral distribution may then rapidly penetrate (transversely) into the preform.
In one embodiment, for increasing the pressure exerted onto the preform, an autoclave (pressure chamber) is used in which the arrangement (“vacuum structure”), comprising tool surface, preform, and covering, is housed.
Apart from the use of such a pressure chamber, which is already known from the prior art, in the context of the present invention the pressure chamber may also be used for simplifying the aforesaid adjustment of the environmental parameters and/or for adding a catalyst for the purpose of deliberately influencing the resin film properties, especially consistency and viscosity. For instance, a gaseous catalyst may be added to the interior of the pressure chamber at a desired stage of the production process. Temperature and pressure (or negative pressure) in particular are physical parameters that may be adjusted in an autoclave for controlling the individual production process steps. A process control may be attained by means of adapting time periods for individual process steps.
As an alternative to a gaseous catalyst, a catalyst in liquid form or e.g. as a powder may also be used. The effect of the catalyst, with nothing further, may remain limited primarily to the exposed resin surface and there ensure that the consolidation (e.g. by polymerization) in this resin area has a head start compared to the underlying resin layers. As stated, these underlying resin layers may be important in the context of the infiltration of the preform (by the resin film material itself).
In one exemplary embodiment the resin film is removed from the cured preform at the end of the production method. Alternatively, it is also possible for the resin film to remain on the cured preform at the end of the method and thus to embody a component of the finished fiber composite component.
It is understood that the specific selection of the matrix material (e.g. epoxide resin system) and also of the fiber material (e.g. fibers made of carbon, glass, synthetic plastic, etc.) is of lesser importance for the fiber composite component in the context of the invention. In one embodiment, the component to be produced is a carbon fiber-reinforced plastic component.
In addition to the aforesaid increases in temperature, in the context of the invention it is also possible to provide cooling in at least one method step in order to deliberately influence the resin film and/or the preform.
Another very advantageous use of the described method is the production of a(n) (open or closed) hollow component by infiltrating and curing, for instance, two or more component preforms in a suitable tool (having a cavity in the tool). During the production of such hollow components, it is advantageously possible by means of the invention to do without the use of relatively complex tools, specifically a “mold core.” Instead, the aforesaid air-tight covering or the resin film may be provided on the interior of the overall hollow preform arrangement to embody an air-tight separation surface that is required to realize the vacuum and/or pressure support and that separates an “interior pressure chamber” from an “exterior vacuum chamber” during production of hollow components.